Article with holographic and retroreflective features

ABSTRACT

An article is disclosed having both holographic and retroreflective features. The article includes a holographic layer that is perceptible under normal lighting conditions and substantially imperceptible to the unaided eye under retroreflective lighting conditions, a retroreflective layer perceptible under retroreflective lighting conditions, and means for bonding the two layers together.

This is a division of application Ser. No. 08/602,637 filed Feb. 16,1996, now U.S. Pat. No. 5,656,360.

FIELD OF THE INVENTION

The invention relates to articles having both holographic features thatare visible under normal lighting conditions, for providing decorationor an indication of authenticity, and retroreflective features that arevisible under retroreflective lighting conditions.

BACKGROUND OF THE INVENTION

A variety of security articles are known in the art. For example, U.S.Pat. No. 5,169,707 (Faykish et al.) discloses a retroreflective securityarticle with dual level verification. Included are primary legends thatare visible under both ordinary diffuse lighting conditions and underretroreflective lighting conditions, and "retrolegends" that areviewable only under retroreflective viewing conditions. Thus, theprimary legend provides a first level of screening or verification underordinary diffuse lighting conditions, without special equipment. Theretro-legends provide a second level of verification underretroreflective lighting conditions, and thus a higher degree ofsecurity for the article as a whole. Although the security articlesdisclosed in the '707 patent have their own utility, they share certainlimitations. Specifically, the primary legend remains visible underretroreflective lighting conditions, which can obscure theretro-legends. Also, the articles disclosed in the '707 patent arenecessarily transparent, so that they may be used over documents such asdriver's licenses, title documents, and passports.

Another conventional security article is disclosed in U.S. Pat. No.4,368,979 (Ruell) discloses an automobile identification systemincluding a license plate having alpha-numeric characters perceptible tothe unaided eye, and a hologram that provides encoded identifyinginformation that cannot be decoded by the unaided eye. Although this,too, can be a useful product for some applications, the fact that anunaided eye cannot decode the holographic information renders the systemmore expensive, and correspondingly less useful for some applications.

In view of the disadvantages associated with these and other knownarticles, such as those disclosed in U.S. Pat. Nos. 3,993,401(Strehlow), 4,036,552 (Lee et al.), and 4,095,875 (Lee et al.), it isdesirable to provide an article having both holographic andretroreflective features, wherein the hologram does not visuallyinterfere with the retroreflective feature.

SUMMARY OF THE INVENTION

The article of the present invention provides enhanced visualrecognition features and improved visual appeal, due to the presence ofboth holographic and retroreflective elements. The inventive article maybe used in a variety of applications, such as a security label for avehicle window, bumper, or license plate, consumer products,identification cards, documents, a tamper-evident seal film, or asheeting for marking bikes, helmets, clothing, traffic signs, licenseplates, and people to improve identification under retroreflectiveconditions.

In one embodiment, the article includes a holographic layer that isperceptible under normal lighting conditions and substantiallyimperceptible to the unaided eye under retroreflective lightingconditions, a retroreflective layer perceptible under retroreflectivelighting conditions, and means for bonding the retroreflective andholographic layers together. Other optional layers may also be included,such as a cover film, a tie layer, an adhesive layer, a heat-shrinklayer, a patterned coating layer with differential adhesion, and indiciapatterns.

BRIEF DESCRIPTION OF DRAWINGS

The invention will be described herein with reference to the appendeddrawings, in which:

FIG. 1 is a cross-sectional view of an embodiment of the inventivearticle, including an enclosed microsphere-type retroreflective layer;

FIG. 2 is a cross-sectional view of a second embodiment of the inventivearticle, also including an enclosed microsphere-type retroreflectivelayer;

FIG. 3 is a cross-sectional view of a third embodiment of the inventivearticle, including an encapsulated microsphere-type retroreflectivelayer;

FIG. 4 is a cross-sectional view of a fourth embodiment of the inventivearticle, including a cube corner-type retroreflective layer; and

FIG. 5 is a cross-sectional view of a fifth embodiment of the inventivearticle, including an enclosed microsphere-type retroreflective layer.

DETAILED DESCRIPTION OF THE INVENTION

The article of the present invention comprises a holographic layer thatis visible under normal lighting conditions but is substantiallyimperceptible to the unaided eye under retroreflective lightingconditions, and a retroreflective layer that is visible underretroreflective lighting conditions. As used herein, the term "normallighting conditions" refers to the presence of ambient light that issubstantially diffused, as with light typically used to light a room.The term "retroreflective lighting conditions" refers to the presence ofambient light that is substantially collimated, as with the light castby the headlight of an automobile, or by a flashlight. The term "unaidedeye" means normal (or corrected to normal) human vision not enhanced by,for example, magnification.

To facilitate a complete understanding of the various aspects of theinventive article, the general construction of the article will bedescribed, followed by descriptions of specific layers, a description ofsuitable methods for making the article, and several illustrativeExamples.

I. General Construction

The article of the present invention includes a holographic layer, whichis preferably a microstructured holographic layer, and a retroreflectivelayer, which preferably comprises either microspheres or cube cornerelements. The article may also include other layers, such as a coverfilm for protecting the article, a tie layer for bonding the layers ofthe article together, an adhesive for bonding the article to the surfaceof an object, a heat-shrink layer for preventing a person from tamperingwith the article by applying heat, a patterned coating layer withdifferential adhesion for providing an indication of tampering bydelamination, and additional indicia visible under various lightingconditions.

II. Holographic Layer

As shown in FIG. 1, the holographic layer 10 comprises two parts: astructured layer 20 and an optional reflective layer 30. The structuredlayer can be formed by several methods that are well known in the art,as disclosed in U.S. Pat. No. 4,856,857 (Takeuchi et al.), the contentsof which is incorporated by reference herein. It may be made ofmaterials such as polymethyl methacrylate, nitrocellulose, andpolystyrene. The structured layer includes a microstructured reliefpattern of holographic or diffraction grating images in the form oflogos or patterns that reflect light. In one embodiment, an embossedmicrostructured layer may be formed by contacting the material fromwhich the structured layer will be made with a non-deformable embossingplate having a microstructured relief pattern, and applying heat andpressure. Alternatively, the structured layer may be made by any othersuitable process, such as radiation curing, and may be made of materialssuch as urethane, epoxy, polyester, and acrylate monomers and oligomers,which are formulated with photoinitiators, cast on a non-deformable toolhaving a microstructured relief pattern, and radiation cured.

The optional reflective layer 30 is coated on the structured layer 20either before or after embossing. The reflective layer preferably has ahigher refractive index than the structured layer. In a preferredembodiment, the reflective layer is substantially transparent andcolorless. Illustrative examples of suitable reflective layer materialsinclude but are not limited to bismuth trioxide, zinc sulfide, titaniumdioxide, and zirconium oxide, which are described in U.S. Pat. No.4,856,857 (Takeuchi et al.). Less transparent materials such as thinaluminum or silver, or patterned reflectors can also be used. Thereflective layer enhances the reflection of light through the structuredlayer due to the difference in refractive index between the structuredand reflective layers. Thus, the structured holographic pattern is morereadily visible to the unaided eye once the reflective layer is coatedon the structured layer, and an adhesive can be directly applied to thestructured layer without diminishing the visibility of the structuredpattern.

III. Retroreflective Layer

Retroreflective layer 50 may comprise one or more types ofretroreflective materials, including microsphere-type retroreflectivematerials and cube corner-type retroreflective materials. As shown inFIG. 1, retroreflective layer 50, as disclosed in U.S. Pat. No.2,407,680 (Palmquist et al.), may comprise an enclosed monolayer ofglass microspheres 60, which are coated in a spacing resin 70comprising, for example, polyvinyl butyral or polyester. The spacingresin conforms to the microspheres. A reflector layer 80 underliesspacing resin 70, and may comprise opaque materials such as silver,aluminum, chromium, nickel, or magnesium, or transparent high-indexreflector materials such as those described above for use on theholographic structured layer, such as zinc sulfide, or multilayerreflectors as described in U.S. Pat. No. 3,700,305 (Bingham). Thus,light that enters the retroreflective layer is focused by the glassmicrospheres through the spacing resin, and reflected by the reflectorlayer back through the spacing resin and glass microspheres to anobserver.

As shown in FIG. 2, an optional beadbond layer 90 may also be provided.In that embodiment, the glass microspheres 60 are coated onto thebeadbond layer 90, and then the spacing resin 70 is coated onto theglass microspheres. The beadbond layer may contain a colored pigment(including black pigment) that gives the retroreflective material acolored appearance in normal light, and the appearance of a differentcolor, such as silver, in retroreflective light. This is describedfurther in U.S. Pat. No. 2,407,680 (Palmquist et al.).

FIG. 3 illustrates an alternate retroreflective layer 50, as disclosedin U.S. Pat. No. 3,801,183 (Sevelin et al.), comprising an exposedmonolayer of glass microspheres 60, and indicia pattern 40 printed onthe back surface of the microspheres, a reflector layer 80 on the backsurface of the printed indicia and the glass microspheres, and abeadbond layer 90. A holographic structured layer 20 without a reflectorcould be sealed over this retroreflective layer to an adhesive film 155to provide an air gap between the structured layer and the microspheresfor both holographic visibility and retroreflection.

As shown in FIG. 4, retroreflective layer 50' may include a multiplicityof cube-corner retroreflective elements 100, instead of glass microspheres and resin, that may be made of materials such as vinyl,polycarbonate, or acrylic for embossed cube-corner retroreflectiveelements, and urethane, epoxy, polyester, and acrylate oligomers andmonomers for radiation-cured cube-corner retroreflective elements. Thecube-corner elements typically have three mutually perpendicular faceswith surface areas of between approximately 1.9×10-3 mm2 to 0.1 mm2.Cube-corner retroreflective elements can be embossed by a master moldinto a sheeting material under suitable temperature and pressure. Theelements may also be created by coating a radiation-curable resin onto amaster mold, laminating an overlay film under sufficient pressure, andsolidifying the resin by curing it with radiation.

Cube-corner retroreflective elements 100 may optionally have areflective coating 105, as shown in FIG. 4. The reflective coating maybe made of the same materials as those previously described formicrosphere retroreflective material, and is typically applied on theback surfaces of the cube comers so that an adhesive or film 155 can bedirectly applied to the cube corners and still allow retroreflection.Also, the cube corner retroreflective elements can be used without areflective coating, and possibly attached to clothing articles by sewingor seating the edges to provide an air gap.

IV. Additional Layers

The holographic layer and the retroreflective layer are typically bondedtogether by a tie layer 120, such as that shown in FIG. 2. Suitablematerials for such a tie layer include primers or adhesives, as either acoating or a film, such as urethanes, olefins, vinyls, and acrylics. Thetie layer may be any appropriate thickness, and may be applied either tothe holographic layer or to the retroreflective layer, or both, prior tobonding those two layers together to make the inventive article.

The tie layer 120 shown in FIG. 2 may be made of a heat-shrink material.In that embodiment, the heat-shrink layer provides protection againsttampering by the application of heat, because the application of asufficient level of heat causes the heat-shrink layer to deform. Thedeformed heat-shrink layer causes the article to deform, and thusprovides an indication of tampering. Polyolefin film is a preferredmaterial for the heat-shrink layer, and may also be used in the articleas a cover film, tie layer, and adhesive.

A durable cover film 140 may also be provided, as shown in FIG. 2, toprotect the article from degradation due to environmental conditions.The cover film may be either a film, including but not limited topolyester, polyvinyl chloride, polyolefin, polycarbonate, or celluloseacetate, or a coating such as an abrasion resistant or durable coating.The cover film may be of any suitable thickness, depending onrequirements for tamper resistance and durability for indoor and outdoorapplications.

For applications in which the article will be bonded to a surface, afacing layer of adhesive 150 may be provided at the light-entrantsurface of the article, as shown in FIG. 1, or an attachment adhesive155 may be located at the bottom of the article, as shown in FIG. 2.Adhesives may include pressure sensitive adhesives, such as acrylics, orheat-activated adhesives, such as polyolefins, polyesters, urethanes,and vinyls. These adhesives are useful for applying the article toplastic, paper, photographs, metal, glass, fabric, and other surfaces,and the amount and type of adhesive may be selected as known in the artto provide the adhesion features desired. Adhesives 150 and 155 may becovered by a removable liner 160, as shown in FIG. 1, to protect theadhesive from contamination prior to application of the article to asurface.

As shown in FIG. 1, an optional patterned coating layer 170 that eitherincreases or decreases adhesion may also be provided to aid in detectingtampering. The patterned coating layer may be provided at or near theinterface of the cover film and holographic layers, or at or near theinterface of the holographic and retroreflective layers. A particularlyuseful application of a patterned coating layer is one in which thatlayer is used adjacent a layer having printed indicia or an arrangementof one or more holographic emblems. When the article is delaminated atthe patterned coating layer, a portion of the printed indicia oremblem(s) remains bonded to each delaminated portion. Thus, an observercan more easily detect whether, and where, someone has tampered with thearticle.

An optional indicia pattern 180, as shown in FIG. 2, can be applied inthe same locations as the patterned coating layer described above, or inother locations within the construction. The indicia pattern or logosare preferably printed with colored inks, pearlescent inks, or inksvisible under ultraviolet light or imaged using toners or dyes in apattern. These colored indicia are especially useful when printed atsome location above the front surface of the retroreflective layer shownin FIG. 2, which has a colored beadbond. In normal light, the colored(preferably black) beadbond hides the colored indicia and only thehologram is typically visible, because the hologram detracts from thevisibility of the colored indicia. However, under retroreflectivelighting conditions, the colored indicia is brightly visible against thebackground, which is preferably silver, and the hologram is no longervisible. Angular indicia 190, as shown in FIGS. 1 and 3, may also beimaged onto the microsphere retroreflective layers according to thelaser imaging process described in U.S. Pat. Nos. 4,688,894 (Hockert)and 4,200,875 (Galanos). Usually, when this process is used to imageenclosed microsphere retroreflective materials with opaque reflectors,or exposed microspheres with transparent reflectors, the indicia arevisible in both normal and retroreflective light. In this invention,using enclosed microsphere retroreflective material with transparentreflectors, the indicia are not visible in normal light but are visibleonly under retroreflection, thus the indicia are hidden until viewedunder retroreflective lighting conditions. Also, the angular indiciathat are usually visible in normal light can effectively be hidden undernormal lighting conditions by using a distracting holographic image overthe retroreflective sheeting.

In FIG. 5, a holographic layer 10 with a structured layer 20 withoutreflectors can be provided over a retroreflective layer 50. Themicrostructured holographic image does not require a reflector if it isexposed to air and is not laminated to another layer.

V. Method of Manufacturing

A preferred method of manufacturing the inventive article is to preparethe holographic and retroreflective portions separately, and then bondthose portions together. The holographic layer may either be prepared byembossing, or by any other suitable process as is known in the art. Theretroreflective layer may be prepared as previously described, and mayinclude either cube corner elements, or glass microspheres, as is alsoknown in the art.

To bond the holographic and retroreflective layers together, aconventional laminating process may be used. Heat and pressure are usedto laminate the layers together with a heat-activated tie layer. Also,if the materials of the holographic and retroreflective layers arecompatible, the layers can be bonded without using a tie layer. Thelayers can either be laminated using continuous contact, such as using asolid steel hot roll, or sealed around the edges to provide an air gapbetween the holographic and retroreflective layers. Alternatively,pressure lamination can be used if the tie layer is a pressure sensitiveadhesive.

VI. Examples

The invention will be further explained by the following illustrativeExamples.

Example One

A transparent article with visible holographic logos, and with hiddenangular logos only visible under retroreflective lighting conditions,was prepared as follows. An enclosed microsphere transparentretroreflective article of the type described in U.S. Pat. No. 5,169,707(Faykish et al.) was used, and comprised a polyethylene-based tie layer,a slurry of glass microspheres with polyvinyl butyral spacing resinbehind the microspheres, a transparent zinc sulfide reflector on theresin, and a polyolefin adhesive layer.

The article was angularly imaged with a neodymium: yttrium aluminumgarnet (Nd:YAG) laser using a process similar to that described in U.S.Pat. No. 4,688,894 (Hockert). The laser power level was adjusted toabout 80 mJ/cm2, with a pulse rate of about 10 pulses per second, andused to image the front of the article through a mask in the shape of a1.0 cm diameter logo at an angle perpendicular to the article. Atransparent hologram film, available from the Crown Roll Leaf Company ofPaterson, New Jersey under the designation XPT, consisting of apolyester cover film, a polystyrene-based structured layer, and ahigh-index zinc sulfide reflector was applied to the front of theretroreflective article using an acrylic pressure sensitive adhesiveavailable from the 3M Company of St. Paul, Minn. under the designationpressure sensitive adhesive 966.

Only the holographic logos were visible under normal lightingconditions; the angular logos were substantially imperceptible to theunaided eye. Under retroreflective lighting conditions, the hologram wasno longer visible, but the angular logos were bright gold and contrastedwith the blue retroreflective background at an angle perpendicular tothe article. When the article was viewed at an angle apart from theperpendicular under retroreflective lighting conditions, the logos wereno longer visible; only a continuous blue background was visible. Asimplified construction in accordance with this Example would consist ofa structured holographic layer, a high-index reflective layer, a tielayer, a bead/resin slurry, a reflector, and an adhesive which could beimaged by a laser through the front side of the article.

This transparent material could be used as a security article overprinted documents, or as a label to protect articles. A pressuresensitive adhesive layer could be applied to the front face of thematerial for use as a transparent label inside windows, which wouldcause minimal distraction of visibility though the window.

Example Two

An opaque article with visible holographic and colored logos and withhidden angular logos visible only under retroreflective lightingconditions was prepared as follows. An enclosed microsphere opaqueretroreflective sheeting was used, consisting of a slurry ofmicrospheres with polyvinyl butyral spacing resin behind themicrospheres, an opaque aluminum reflector on the resin, and an acrylicpressure sensitive adhesive layer. This construction is available fromthe 3M Company of St. Paul, Minn. under the designation 3750 sheeting.The front of the sheeting was printed with red, blue, and black coloredlogos. The sheeting had also been imaged at an angle apart from theperpendicular with a laser using a process similar to that described inU.S. Pat. No. 4,200,875 (Galanos). The transparent hologram described inExample One was applied to the front of the retroreflective sheetingusing a pressure sensitive adhesive.

The holographic logos were visible under normal lighting conditions, anddid not distract from the visibility of the colored logos, but theangular logos were partially hidden by the holographic logos because thehologram detracted from their visibility. Under retroreflective lightingconditions, the hologram was no longer visible, but the colored logoswere brightly visible against the silver retroreflective background.When the sheeting was viewed at an angle apart from the perpendicularunder retroreflective lighting conditions, the angular logos werevisible as black over the silver retroreflective background.

This article could be used as a label to protect articles, or with aface adhesive for application to a window. The article could also beused as a license plate sheeting, because the entire area retroreflectsunder the holographic image. A smaller label of the transparent hologramdescribed in Example 1 could be applied as a validation label over aportion of a retroreflective license plate.

Example Three

An opaque article with visible holographic logos, and with hiddencolored logos only visible under retroreflective lighting conditions wasprepared as follows. An enclosed microsphere retroreflective sheetingthat appeared black under normal light and silver under retroreflectivelighting conditions, as described in U.S. Pat. No. 2,407,680 (Palmquistet al.), was used. It consisted of a clear vinyl top film, glassmicrospheres dispersed in black resinous beadbond, a polyvinyl butyralspacing resin behind the microspheres, an aluminum reflector on theresin, and an acrylic pressure sensitive adhesive layer. The front ofthe sheeting was printed by hand with colored logos using red, blue, andblack permanent marking pens. The transparent hologram described inExample One was applied to the front of the retroreflective sheetingusing a pressure sensitive adhesive.

Only the holographic logos were visible under normal lightingconditions, and the colored logos were substantially imperceptible tothe unaided eye. Under retroreflective lighting conditions, the hologramwas no longer visible, but the colored logos were brightly visible onthe silver retroreflective background. The angular imaging methods fromExamples 1 & 2 could be used to provide hidden angular logos onlyvisible under retroreflective lighting conditions.

Example Four

An article was made using tamper-indicative film of the type describedin U.S. Pat. No. 5,153,042 (Indrelie) to improve the tamper-resistanceof the construction, consisting of a polyester cover layer, a patternedrelease coating, and a polyester resin primer layer. A hologram having astructured layer and a high-index zinc sulfide reflector was applied tothe primer layer using heat lamination. An acrylic pressure sensitiveadhesive was used to attach the hologram to the front of theretroreflective sheeting. The article had the following sequentiallayers: a polyester cover layer, a patterned release coating, a primerlayer, a structured hologram, a high-index reflector, a pressuresensitive adhesive tie layer, and a retroreflective layer of the typedescribed in Example Two. The article was applied to a plastic videocassette as a label. When this article was peeled at room temperature,the patterned release coating provided tamper evidence by splitting thehologram layer in the release pattern between the polyester cover layerand retroreflective layer.

Example Five

An article was made to provide a fragile and tamper resistantconstruction, and included a thin transfer hologram that was hotlaminated to the front of a retroreflective sheeting with a patternedrelease coat. The thin transparent hologram transfer film, such as VT55available from Crown Roll Leaf, Inc. of Paterson, N.J., consisted of apolyester liner, a polymethyl methacrylate based structured layer, ahigh-index zinc sulfide reflector, and a thin adhesive. The enclosedmicrosphere opaque retroreflective sheeting contained apolyethylene-acrylic acid-based tie layer on the front surface of theretroreflective layer from Example Two, which was printed with a releasepattern of urethane resin, and then laminated with the thin hologram.The polyester liner was removed from the hologram, and a pressuresensitive adhesive on a silicone liner, available from the 3M Companyunder the designation pressure sensitive adhesive 9457, was applied tothe hologram side as a face adhesive. The finished constructionconsisted of the silicone liner, pressure sensitive adhesive, structuredhologram, a high-index reflector, thin adhesive, urethane-based releasepattern, polyethylene-based tie layer, a bead/resin slurry, an aluminumreflector, and a polyolefin backing layer. The silicone liner was peeledfrom the pressure sensitive adhesive and the construction adhered to theinside window of a vehicle. The hologram and retroreflective layer werevisible from the outside of the window. The thin transferred hologramwas destroyed by splitting in the release pattern when peeled from thewindow, so that the label could not be removed and reused in anothervehicle. In a different embodiment, the thin adhesive layer on thehologram could be eliminated to simplify the construction.

Example Six

Another article with tamper resistance was made as follows. The thintransfer hologram used in Example Five was laminated to an ethyleneacrylic acid-based pattern of adhesion promoter printed on polyvinylbutyral-based retroreflective base from Example Two. The constructionhad sequential layers of a silicone liner, pressure sensitive adhesive,a structured hologram, high-index reflector, thin adhesive, adhesionpromoting pattern, a bead/resin slurry, reflector, and backing. Afterapplication to a window, the hologram was destroyed by splitting in theadhesion promoter pattern when peeled.

Example Seven

An article was made by sealing a hologram layer over a retroreflectivelayer with exposed glass microspheres. A retroreflective layer, asdescribed in U.S. Pat. No. 3,801,183 (Sevelin et al.), was used. Thetransparent hologram film from Example 1 was sealed over the microspherelayer and attached to a pressure sensitive adhesive surrounding themicrosphere area, to provide areas of contact for adhesion, which areadjacent to areas with an air gap over the microspheres to allowretroreflection. The holographic layer does not require a high-indexreflector. The construction had sequential layers of a cover layer, astructured layer, a high-index reflector, an air gap between sealedareas of the holographic and retroreflective layers, microspheres, anindicia, high-index reflector on the microspheres, beadbond resin, andan adhesive. A simplified construction would include a structured layer,an air gap, microspheres, a reflector, and beadbond.

Example Eight

A transparent hologram, either the polyester-based film from Example Oneor a thin transfer film from Example Five, could be laminated over cubecorner retroreflective sheeting. Like previous Examples, the hologramwould be visible under normal lighting conditions, and the constructionwould still be retroreflective, because the hologram would notsignificantly reduce the retroreflective brightness.

Various modifications and combinations of the embodiments disclosed willbe apparent to those skilled in the art, and those modifications areintended to be within the scope of the invention as defined in theappended claims.

We claim:
 1. An article comprising:(a) a transparent holographic layerperceptible under norm al lighting conditions , and substantiallyimperceptible to the unaided eye under retroreflective lightingconditions; (b) a retroreflective layer, comprising a multiplicity ofcube corner retroreflective elements, that is perceptible underretroreflective lighting conditions; and (c) an indicia layer.
 2. Thearticle of claim 1, wherein the article further includes at least one ofa cover film, a tie layer, an adhesive layer, a heat-shrink layer, and apatterned coating layer with differential adhesion.
 3. The article ofclaim 1, wherein the article includes more than one of a cover film, atie layer, an adhesive layer, a heat-shrink layer, and a patternedcoating layer with differential adhesion.
 4. The article of claim 1,wherein the article includes a holographic layer comprising a structuredlayer on an exposed surface of the article.
 5. The article of claim 1,wherein the article includes a holographic layer comprising a structuredlayer and a substantially transparent reflector layer.
 6. The article ofclaim 5, wherein the transparent reflector layer is a discontinuouspattern of reflective material.
 7. The article of claim 5, wherein thetransparent reflector layer is a material with a higher refractive indexthan the structured layer.
 8. The article of claim 5, wherein theindicia layer is formed on the cube corner portions of theretroreflective layer, and is substantially imperceptible to the unaidedeye under normal lighting conditions, but is perceptible underretroreflective lighting conditions.
 9. The article of claim 8, whereinthe indicia is a pattern of reflective material that contrasts inbrightness with its background under retroreflective lightingconditions.
 10. The article of claim 9, further including an adhesivelayer for bonding the article to a surface.
 11. The article of claim 8,wherein the indicia is a pattern of non-reflective material thatcontrasts in brightness with its background under retroreflectivelighting conditions.
 12. The article of claim 1, wherein the indicialayer is disposed between the holographic and retroreflective layers.13. The article of claim 1, wherein the holographic layer is between theindicia layer and the retroreflective layer.
 14. The article of claim 1,wherein the retroreflective layer is between the holographic layer andthe indicia layer.
 15. The article of claim 1, wherein the indicia layeris disposed between the holographic layer and the retroreflective layerso that the indicia is substantially imperceptible to the unaided eyeunder normal lighting conditions, but is perceptible underretroreflective lighting conditions.
 16. The article of claim 15,wherein the retroreflective layer contains a continuous reflector on thecube corner portions of the retroreflective layer, which is bright underretroreflective lighting conditions and dark under normal lightingconditions.
 17. The article of claim 16, further including an adhesivelayer for bonding the article to a surface.
 18. The article of claim 17,further including a patterned differential adhesion layer disposedbetween the retroreflective layer and the adhesive layer.
 19. An articlecomprising:(a) a transparent holographic layer perceptible under normallighting conditions, and substantially imperceptible to the unaided eyeunder retroreflective lighting conditions; (b) a retroreflective layerthat is perceptible under retroreflective lighting conditions; and (c)an indicia layer; (d) a patterned differential adhesion layer; and (e)an adhesive layer underlying the patterned differential adhesion layer,to bond the article to a surface.